A detailed study has been conducted of the effects of LiCI, NaCI, KCI, RbCI, CsCI, KOH, and K2CO3 on the steam gasification of char produced from a western sub-bituminous coal. Initial screening of results revealed that K2CO3 had the greatest catalytic activity for a fixed cation content in the char. Subsequent experiments were performed to determine the effects of K2CO3 loading and gasification temperature on the rate of gasification and the product-gas composition. The results show that gasification rate is enhanced with increasing K2CO3 loading and reaction temperature. Increasing K2CO3 loading causes CO to be formed in preference to CO2 and H2 and suppresses the production of CH4. Increasing temperature also causes CO to be formed in preference to CO;! and H2 but enhances the production of CH4. These results are discussed in the light of a mechanism to explain the unique catalytic behaviour of K2CO3.
Use of a catalyst to accelerate the steam gasification of coal is highly attractive since it offers the possibilities of operating gasifiers at higher coal throughputs and lower temperatures than are practicable in the absence of a catalyst. Screening studies performed by a number of investigators'-" have revealed that the most effective catalysts are alkali metal salts and that for a given cation the associated anion has an important role. Thus, it is generally concluded that oxides, hydroxides, bicarbonates, and carbonates are more active than other salts. Reasons for the higher activity of these compounds and the mechanisms by which they promote gasification have not been clearly established.
The objective of the present study was to investigate in detail the effects of alkali metal salts and in particular of K2CO3 on the steam gasification of char derived from a western sub-bituminous coal. lnstantaneous gasification rates and gas production rates were measured as a function of catalyst type, catalyst loading, and reaction temperature. For the case of K2CO3, possible mechanisms have been proposed to explain the role of this catalyst in accelerating gasification and controlling the distribution of gaseous products.